The present invention relates to methods and compositions for reducing proppant and particulate flow-back, (referred to herein collectively as “particulate migration”). More particularly, the present invention relates to the use of novel silicone matrixes for reducing particulate migration in subterranean formations, for example, during fracturing and production operations.
Hydraulic fracturing is a process commonly used to increase the flow of desirable fluids from a portion of a subterranean formation. Traditional hydraulic fracturing operations comprise placing a fracturing fluid into a portion of a subterranean formation at a rate and pressure such that fractures are formed or enhanced into the portion of the subterranean zone. The fractures tend to propagate as vertical and/or horizontal cracks located radially outward from the well bore. In such treatments, once the hydraulic pressure is released, the fractures formed will tend to close back onto themselves. To prevent this, oftentimes particulate materials, known as proppant, are placed in the fractures by transporting them in the fracturing fluid during at least a portion of the fracturing operation. The particulates are carried into the created or natural fractures and deposited therein such that when the hydraulic pressure is released the particulates act to prevent the fracture(s) from fully closing, and thus, aid in forming conductive channels through which produced fluids may flow into the well bore. Without the proppant particulate materials, the fractures tend to close and reduce permeability gained by the fracturing operation. The term “propped fracture” as used herein refers to a fracture (natural or otherwise) in a portion of subterranean formation that contains some proppant particulates. The proppant particulates in a fracture often consolidate to form a proppant pack. The term “proppant pack” refers to a collection of a mass of proppant particulates within a fracture. Proppant packs can minimize the flow-back of proppant from the fractures. Oftentimes, the proppant particulates are coated with a substance (e.g., a resin, a tackifying agent, or the like) that enables them to form proppant packs more easily.
Hydrocarbon wells are often located in subterranean zones that contain unconsolidated particulates (e.g., proppant and formation fines) that may migrate within the subterranean formation with the oil, gas, water, and/or other desirable fluids produced by a well. The presence of these unconsolidated particulates in produced fluids generally is disadvantageous and undesirable in that the particulates may abrade pumping and other producing equipment and reduce the fluid production capabilities of producing zones. The particulates also may impact negatively the permeability of the formation. Unconsolidated subterranean formations include those that contain portions that contain loose particulates (e.g., proppant and formation fines) and those wherein the bonded particulates have insufficient bond strength to withstand the forces produced by the production of fluids through the zones.
One traditional method of controlling particulate migration in zones of a subterranean formation involves placing a filtration bed containing gravel particulates near the well bore that neighbors the zone that contains unconsolidated particulates. The filtration bed acts as a sort of physical barrier to the transport of unconsolidated particulates to the well bore that could be produced with the produced fluids. Typically, such so-called “gravel packing operations” involve the pumping and placement of a quantity of desired particulates into the unconsolidated formation in an area adjacent the well bore. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The sand control screen is generally a filter assembly used to retain the gravel placed during a gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated particulates. Oftentimes, the gravel particulates are coated with a substance (e.g., a resin, a tackifying agent, or the like) that enables them to form gravel packs more easily. The resulting gravel pack presents a barrier to migrating sand from the formation while still permitting fluid flow. When installing the gravel pack, the gravel is carried to the annulus in the form of a slurry by mixing the gravel with a fluid, often known as a “gravel pack fluid.” Sometimes gravel pack fluids are viscosified with suitable gelling agents. Once the gravel is placed in the well bore, the viscosity of the fluid is reduced, and it is returned to the surface. In some gravel packing operations, commonly known as “high rate water packing operations,” the fluid has a lower viscosity and yet the gravel is transported because the treatment occurs at a high velocity. Gravel packs act, inter alia, to stabilize the formation while causing minimal impairment to well productivity. The gravel, inter alia, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Such packs may be time consuming and expensive to install.
Another similar method involves applying a non-aqueous tackifying composition to the unconsolidated particulates in an effort to reduce the migration of particulates within the zone. Whereas a curable resin composition produces a hard mass, the use of a non-aqueous tackifying composition produces a more malleable consolidated mass that retains a tacky character. One potential disadvantage associated with such systems is that because of their tackiness and tendency to stick to surfaces, significant amounts of the material may be lost by absorption to undesired surfaces during placement. Another alternative is an aqueous tackifying composition. Aqueous tackifying compositions, however, have their own problems including, but not limited to, the fact that they usually require external activators and surfactants for optimum performance. One problem associated with tackifying agents is that they tend to leach out of the desired area once placed in the formation. This leaching may be due to partial solubility in produced fluids or to dislodgement from the surfaces by flowing fluids or abrasive action of particulates in the produced fluids.
In some instances, it may be desirable to use both a resin and a tackifying composition together to obtain the benefits of both a resin and a tackifier. For example, if the tackifying agent is aimed at coating the formation surfaces to trap the fines, any fines that are not trapped by the tacky formation surface would flow with the produced fluids. However, if the proppant itself is rendered tacky either exclusively or in addition to coating the formation with tacky materials, then any fines that are not trapped by the formation surface will be trapped by the tacky proppant surface. The latter process may be more effective because proppant is thought to offer more flowing surface to a flowing fluid due to increased tortuosity in the flow path, thus increasing the probability of trapping the fines in the produced fluid. However, this is not usually possible because the tackifying agent reacts with the resin so that it becomes hardened, and does not remain tacky as desired. Since it does not remain tacky, it may not help with fine migration as intended.